Sewage Treatment Plant

Pre-treatment (Screening and Grit Removal):

• Screening: Large debris such as rags, plastics, and other solids are removed through coarse screens.
• Grit Removal: In this step, heavy particles like sand and other gritty materials are settled out, preventing damage to equipment and reducing clogging.

Primary Treatment:

• Involves the removal ofsuspended solidsandorganic matter.
• The sewage flows into large tanks where solids settle to the bottom, and lighter substances like oils and grease float to the surface and are skimmed off.
• This phase removes about 60-70% of the suspended solids and a small portion of organic pollutants.

Secondary Treatment (Biological Treatment):

• The primary-treated effluent is then subjected tobiological treatmentto remove dissolved and suspended organic matter.
• Activated Sludge Process: The effluent is aerated (air is pumped in) to encourage the growth of microorganisms that break down organic pollutants. The microbes digest the organic material, converting it into biomass (sludge).
• Trickling Filters: Alternatively, wastewater may pass over a bed of bacteria-laden material that breaks down the organic matter.
• This process significantly reduces the Biological Oxygen Demand (BOD) and chemical oxygen demand (COD), which indicates the level of pollution in the water.

Tertiary Treatment (Advanced Treatment):

• After secondary treatment, further treatment may be needed, depending on the quality of the effluent and the intended use of the treated water.
• Filtration: Sand filters or membrane filters are used to remove any remaining fine particles.
• Disinfection: To eliminate harmful pathogens, the treated water may undergochlorinationor be treated withUV (Ultraviolet) light.
• In some cases, processes likereverse osmosisoractivated carbon filtrationare used for high-quality effluent, particularly if the treated water is intended for reuse.

Sludge Treatment:

• The sludge produced during primary and secondary treatment is thickened and processed. It may be further treated through:
  • Anaerobic Digestion: Microorganisms break down organic matter in the absence of oxygen, producing biogas (which can be used for energy).
  • Dewatering: Sludge is dewatered using centrifuges, filter presses, or drying beds.
  • Composting: In some cases, the treated sludge can be composted to reduce volume and create a useful byproduct.

Final Disposal or Reuse:

• After treatment, the effluent can be safely discharged into rivers, lakes, or oceans, or reused for purposes such as agricultural irrigation, industrial cooling, or landscaping.
• The treated sludge is either landfilled, composted, or used for other beneficial purposes, depending on its final quality.